If you examine animal behavior at even the most basic level, basic morality is revealed. Interspecies killing is both rare, and frowned upon. A herd of lions, for example, will box to solve civil problems (say, territorial rights), but these duels are controlled conflicts that seldom result in death. You will not see a pair of lionas randomly kill oneanother without reason or cause. Not so far as human observation or studies of animal behavior have revealed.
Morality itself is nothing but an evolutionary necesity included to allow herd species to function productively. On his own, primitive man was incapable of survival. Sure, if he lived alone, hunted alone, etc. he would not have had to share the fruits of his labor with the rest of the tribe. However, he would not have survived.
So man did not operate as a solitary species; he accepted the requirement for cooperation with his fellow hominids. And in order for these tribes to function and work appropriately, certain basic precepts must be established, namely that murder and theft are unacceptable. This is not some higher undersanding of an individuals right to life; its basic herd survival instinct. If two members of the herd kill one another, the herd as a whole is weakened. Similarly, if the herd cannot rely on its members to fairly distribute the spoils of its labors, the herd cannot productively function. All law is a simple extrapolation from this basic foundation: protection from force and fraud. One might look at modern law as a great departure from core natural law, but if you examine the justifying logic behind it, the connection holds.
Psychology tells us that those incapable of differentiating between right and wrong, at the raw and most fundamental level, are not "natural" results, any more than any other deformity (mental or otherwise) can be considered natural. They are broken; the goal is finding out why, and how. Usually, this is dependent on some form of abuse or great stress, be it mental or physical, prior to and during childhood. If they were deemed "ok" by natural selection, human beings would not have an instinctual revulsion to such deformity.
My point above was to demonstrate that when human beings commit crimes, they do not necesarrily do so because they are "evil" at some basic level, but because they were under the impression that:
A, the benefit of their crimes outweighed the cost.
B, they did not fully consider the ramifications of their actions.
or, rarely, C, they were incapable of appreciating the basic social morality that holds society, defined as cooperating men, together.
Therefore, humans must have the means of preventing the above three scenarios from occuring, since this is counterproductive to the concept of social survival.
